A Record of Atmospheric Co2 During the Last 40,000 Years from the Siple Dome, Antarctica Ice Core

We have measured the CO2 concentration of air occluded during the last 40,000 years in the deep Siple Dome A ( hereafter Siple Dome) ice core, Antarctica. The general trend of CO2 concentration from Siple Dome ice follows the temperature inferred from the isotopic composition of the ice and is mostly in agreement with other Antarctic ice core CO2 records. CO2 rose initially at similar to 17.5 kyr B. P. ( thousand years before 1950), decreased slowly during the Antarctic Cold Reversal, rose during the Younger Dryas, fell to a local minimum at around 8 kyr B. P., and rose continuously since then. The CO2 concentration never reached steady state during the Holocene, as also found in the Taylor Dome and EPICA Dome C ( hereafter Dome C) records. During the last glacial termination, a lag of CO2 versus Siple Dome isotopic temperature is probable. The Siple Dome CO2 concentrations during the last glacial termination and in the Holocene are at certain times greater than in other Antarctic ice cores by up to 20 ppm (mumol CO2/mol air). While in situ production of CO2 is one possible cause of the sporadic elevated levels, the mechanism leading to the enrichment is not yet clear.

Snow Accumulation Rate on Qomolangma (Mount Everest), Himalaya: Synchroneity With Sites Across the Tibetan Plateau on 50-100 Year Timescales

Annual-layer thickness data, spanning AD 1534-2001, from an ice core from East Rongbuk Coll on Qomolangma (Mount Everest, Himalaya) yield an age-depth profile that deviates systematically from a constant accumulation-rate analytical model. The profile clearly shows that the mean accumulation rate has changed every 50-100 years. A numerical model was developed to determine the magnitude of these multi-decadal-scale rates. The model was used to obtain a time series of annual accumulation. The mean annual accumulation rate decreased from similar to 0.8 m ice equivalent in the 1500s to similar to 0.3 m in the mid-1800s. From similar to 1880 to similar to 1970 the rate increased. However, it has decreased since similar to 1970. Comparison with six other records from the Himalaya and the Tibetan Plateau shows that the changes in accumulation in East Rongbuk Col are broadly consistent with a regional pattern over much of the Plateau. This suggests that there may be an overarching mechanism controlling precipitation and mass balance over this area. However, a record from Dasuopu, only 125 km northwest of Qomolangma and 700 m higher than East Rongbuk Col, shows a maximum in accumulation during the 1800s, a time during which the East Rongbuk Col and Tibetan Plateau ice-core and tree-ring records show a minimum. This asynchroneity may be due to altitudinal or seasonal differences in monsoon versus westerly moisture sources or complex mountain meteorology.